Driving device of electronic watch

ABSTRACT

A driving device for an electronic timepiece including a multipole stepping motor driven by an alternative pulse generator operating under the control of a time standard oscillator. The timepiece includes a time indicating gear train including an indexing mechanism having a pawl and a ratchet wheel attached to the second wheel of said train to insure the incremental step action of said stepping motor.

United States Patent w13,597,915

[72] Inventors Susumu Maw: 5 Rderences cited )616 Tlkll, Shlmosuua-machi SIIWI- UNITED STATES PATENTS 2 988 868 6/196! Lavet et al. 58/23 Yoshllumi Gorni. 6248-1. Nishlchlno, Miyn'w Chimnhi' of Nasal), 3,250,066 5/1966 Engelhardt et al 58/23 Japan Primary Examiner-Richard B. Wilkinson [Zl] Appl. No. 873,224 Assistant Examiner-Edith C. Simmons [22] Filed Nov-3,1969 Attorney-Blum, Moscovitz. Friedman & Kaplan [451 Patented- Aug. 10, I971 [32] Priority Nov.$, 1968 [33] Japan [3 1] 43/805 [54] gag WATCH ABSTRACT: A driving device for an electronic timepiece inu eluding a multipole stepping motor driven by an alternative [52] US. Cl. 58/23 D, pulse generator operating under the control of a time standard 310/83 oscillator. The timepiece includes a time indicating gear train [5|] Int. Cl. G04c 3/00 including an indexing mechanism having a pawl and a ratchet [50] Field olSearch 58/23, 23 wheel attached to the second wheel of said train to insure the D, 26.5, 26.6, 27; 3 l0/83 incremental step action of said stepping motor.

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\ TIME STANDARD OSCILLATOR Patented Aug. 10, 1971 3,597,915

4 Sheets-Sheet 1 Patented Aug. 10, 1971 v 3,597,915

4 Sheets-Sheet 8 Patented Aug. 10, 1971 3,597,915

4 Sheets-Sheet S 4 Sheets-Sheet 1 L JFB/ ALTERNATIVE PULSE GENERATOR TIME STANDARD OSCILLATOR "fluctuation'occurs on the second hand due to the fact that 'reverse torque is not applied on the secondhand wheel. A

tion hereafter).

' In explaining the action of the step motor with radial pole the side of stator 2, and an attractive force acts on the rotor at s the stator 1 side. Then the pole 6 of the rotor 4 rotates to the tion ofone step to end. After that, the current in the driving I coil 3 changes its direction alternately in correspondence with the output signal of time standard oscillator such as the quartz I I OF ELECTRONI BACKGROUND OF- THE INVENTION This invention relates to an electromechanical converter of an electronic watch and the like, particularly concerning an improvement of a step motor.

The object of this invention, is in an inductance-type step motor containing a permanent magnet in its rotor, to reduce the vibration that disturbs the norr'nalrotation of the rotor occurring after each step rotation, which has been a defect of the step motor.

, Another object of this invention is to decrease the electric power consumption considerably. Namely, in using the step motor as a converter for electronic watches such as a quartz watch, especially a wrist watch controlled by-quartz crystal, it

- is required that, in'order to actuate such watches perfectly throughout a year, the maximum electric power consumption allowable as a convert'er is less than 8uW. Therefore, a step motor withelectric power consumption below 8pW must be offered. I

In watches wherein electric energy is converted into a relative. rotation of the escapement by'means of electric motor,

furtherobject of the invention isto eliminate the fluctuation of the second hand and to stop the second hand precisely in a predetermined position.

Baler EXPLANATION or DRAWINGS FIG. I is adrawing which shows a step motor hitherto used;

. FIG. 2 is a drawing in'which an indexing mechanism is addedtothestep motorshown in FIG. I;

FIG; 3 to FIG. 8 aredrawings which show characteristics of a step motor; and

FIG. 9 is a drawing which shows an embodiment of step 'motor according .to this invention. cDESCRIP'lION OF THE PREFERRED EMBODIMENTS In the construction of ahitherto-used motor without an indexing mechanism shown in FIG. 1, l, and 2are stators, 3 is a driving coil, 4 is a rotor comprising at least one permanent .magnet having at its periphery a series of alternate North and Southmagnetic poles, and 5 is a rotating shaft of the rotor 4. As shown in the figure, the stators l, 2 areal-ranged eccentrically'and determine the rotating direction of the rotor 4. In the absence of current through the coil 3, the rotor 4 is stably at rest at a position with an inclination at 2 from the center line A-A' of the stators l, 2 (to be called a statically stable posi-' rotor, it is assumed that the poles 1, 3, '5 of the rotor are N- polesand the poles 2, 4, 6 are S-poles. If a pulsive current is applied on the driving coil 3 in such a way that the stator l and the stator 2 are magnetized to be N-pole and S-pole respectively, the rotor 4' is rotated counterclockwise from its statically stable position and stabilized at a position of 13 from the centerline A-A' (to be called a magnetically stable position hereafter). When the current of the driving coil 3 is stopped, the rotor 4 becomes stable again at its original statically stable position, and the stepping motion of the rotor 4 is not performed. Next, if a pulsive current is applied to the driving coil 3 in such a way that the stator l is magnetized to be S-pole and the stator 2 to be N-pole. A pulsive force acts on the rotor at magnetically stable position of B". When the current is stopped after rotating 13, the pole 6 rotates further to the statically stable position of 01, and becomes stable to bring the accrystal oscillator.

The a reverse impulse is applied, the rotor 4 is learning to continue a step rotation in one direction.

' magnetically stable position,

' and the consumed electric power to 6p.w. A similar result can However, in such aconstruction the rotor 4 vibrates around the magnetically stable position until it becomes stable at the and it is necessary to continue the flow of electric current in the driving coil 3 until the time when the said vibration is stopped, resulting in a large electric power consumption.

The action of said vibration will be explained referring to FIG. 3 and FIG. 4. When a pulse is applied on the driving coil .3 so as to make the rotor 4 rotate in the normal direction of rotation, a graph of the output torque vs. the rotation angle of the rotor is approximately obtained experimentally as shown in FIG. 3. Solving the equation of motion, we have, from FIG. 3,

0,: angle from the statically stable position to the magnetically stale position after one step,

0 rotating angle, in one step (angle from the statically stable position to that after one step), T output torque,

T load torque,

J: inertia of rotor, and in case of no-Load, a vibration as shown in FIG. 4 takes place around a point b (magnetically stable position).

FIG. 5 shows a graph obtained from an experimental investigation about the action of the rotor 4. Namely, taking the voltage on the ordinate and the time (t) of actuating the driving coil 3 on the abscissa,is the region'where the rotor 4 makes one-step rotation accurately;is the region where the rotor 4 makes two-step rotation at one time, which occurs due to the fact that the pulse'is cut off before the braking force for the rotation of the rotor is not applied or not sufficiently applied;'is the region where the rotor 4 makes rotation by one step because the braking force is applied well;fi)is the region where an instability appears due to the vibration of the rotor 4, in which the rotor 4 may sometimes return to its original position due to its own vibration; andis the region where the vibration of the rotor 4 is stopped, thereby the rotor 4 becomes stable in a magnetically stable position to be steadily shifted byone step. These-phenomena can be observed by the waveforms of current induced in the driving coil 3 as shown in FIG. 6 in which it is seen that the rotor 4 makes vibration in the regions, while in the regionthe vibration is attenuated. Therefore, in the process of FIG. I it is needed to actuate the rotor 4 in the regionsmand further, as the regions@ are narrow, the driving current should be increased to the regionresulting in a large consumption of electric power.

FIG. 2 a construction in which to the construction shown in FIG. 1 an indexing mechanism is added, wherein a ratchet wheel 16 is mounted coaxially on a rotor shaft and also a reversed rotation preventing spring 17 is provided. The action of the rotor becomes quite'different from that in FIG. 1 owing to the installation of the indexing device.

FIG. 7 gives a waveform of current induced in a driving coil 13 in which the aspect that the vibration of the rotor 4 is shown. From this figure it is seen that, even in the region@) shown in FIG. 5, the rotor 4 does not vibrate and steadily makes its action by one step. Namely, in the construction of FIG. 2 it makes possible to use at any position in the regions@ @Qenabling the driving pulse width to be reduced to a large extentwith decrease of the consumed electric power.

According to an example of experiment, it is found that, in the construction shown in FIG. 1, the minimum pulse width is 45 msec. and the electric power consumption amounts to a l5p.w. necessarily, while in the construction shown in FIG. 2, it is possible to reduce the minimum pulse width to 18 msec.

be obtained in an embodiment of this invention shown in FIG. 9; namely, in the construction of the motor shown in FIG. I,

rotor pinion 28 is mounted on a rotating shaft 25 that is coaxial with arotor 24, and a large toothed wheel 30 engaged with the second hand 29 is attached; i v The rotor24 is provided with 3 pairs of poles and the ratio of the rotation-of the rotating shaft 25 of the rotor 24 to that of 7 the pinion28 is mounted on a second hand shaft 33 on which n large toothed wheel 30 and the rotor pinion 28, so that the vibration that damages the step action of the rotor 24 can be prevented.

Such an aspect may be understood from the waveform of current induced by the driving coil shown in FIG. 8 by the fact that comparing to the waveform induced by the driving coil 3 in the construction of FIG. I, the harmful vibration in the rotor 24 is reduced. Consequently, by applying on the driving coil 23 reverse pulses in which thedirection of-current changes alternately in correspondence with the'output of the time standard generator once a second for a very short time, the second hand can rotate precisely at intervals of l sec. with a slight consumption of electric power.

' Furthermore, since in this construction the indexing mechanism is mounted on the second hand shaft provided with a second hand, a defect caused from the absence of a torque to be constantly applied on the second hand shaft in the process of energy transfer as in a mechanical watch using a spring, that is, a fluctuation of the second hand due to the backlash of time indicating train, is eliminated, so that the unsteadiness of-the stopping position of the second hand can be regulated normally. Therefore, in the construction of FIG. 9

showing an embodiment according to this invention, the harmful vibration that impedes the step action of the rotor is reduced to make the-action steadfast, at the same time, the

' electric power consumption'is decreased, and further the flucbrought to a regular position, resulting in a steady motion of the second hand with a remarkable effectiveness.

Whatweclaimis: m

l. A driving device for an electronic timepiece comprising a time standard oscillator; an alternative pulse generator for generating periodical alternative pulses under the control of said time standard oscillator; stepping motor means operatively coupled to said alternative pulse generator; saids tepping motor means including a stepping rotor havingat its periphery a series of more than two pairs of alternate N and S magnetic poles and a stator having at least two pairs of poles, said stator being arranged coaxially with said rotor, said stepping motor means being adapted to produce alternative polarities on said stator poles to provide a rotating force in one direction on said rotor for the stepwise rotation of said rotor in one direction in response to the output of saidalternative pulse generator; and

by indicating gear train means, said gear train means including a second wheel, means for rotating said second wheel in response to thestepwise rotation of said stepping motor means rotor, and indexing means, said indexing means including a ratchet wheel secured to said second wheel and an indexing pawl in cooperative engagement with said ratchet wheel for controlling the stepwise rotation of said second wheel and stepping motor means rotor.

2. A driving device as recited in claim 1, including further indexing means, said further indexing means including a further ratchet wheel secured to said stepping motor means rotor and a furtherindexing pawl in cooperative engagement with said further ratchet wheel for aiding in the regulation of the stepwise rotation of said rotor. 

1. A driving device for an electronic timepiece comprising a time standard oscillator; an alternative pulse generator for generating periodical alternative pulses under the control of said time standard oscillator; stepping motor means operatively coupled to said alterNative pulse generator; said stepping motor means including a stepping rotor having at its periphery a series of more than two pairs of alternate N and S magnetic poles and a stator having at least two pairs of poles, said stator being arranged coaxially with said rotor, said stepping motor means being adapted to produce alternative polarities on said stator poles to provide a rotating force in one direction on said rotor for the stepwise rotation of said rotor in one direction in response to the output of said alternative pulse generator; and time indicating gear train means, said gear train means including a second wheel, means for rotating said second wheel in response to the stepwise rotation of said stepping motor means rotor, and indexing means, said indexing means including a ratchet wheel secured to said second wheel and an indexing pawl in cooperative engagement with said ratchet wheel for controlling the stepwise rotation of said second wheel and stepping motor means rotor.
 2. A driving device as recited in claim 1, including further indexing means, said further indexing means including a further ratchet wheel secured to said stepping motor means rotor and a further indexing pawl in cooperative engagement with said further ratchet wheel for aiding in the regulation of the stepwise rotation of said rotor. 